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Genomic Evolution of HIV
Overview HIV, or the Human Immunodeficiency Virus, is a retrovirus that causes acquired immunodeficiency syndrome (AIDs). AIDs leads to failure of the immune system, which allows opportunistic pathogens or cancers to develop (2). HIV is a retrovirus, more specifically a lentivirus, which means that it has an RNA genome and can reverse transcribe its own genome, then integrate within the host's DNA. HIV is transmitted through bodily fluids, but cannot thrive outside of host cells. HIV is the fastest evolving virus that has been studied; with the ability of rapidly mutating its genome, the cure for HIV has still not been found (1). HIV Genome HIV is a retrovirus, which means that has a RNA genome. HIV uses reverse transcriptase to revert back to DNA from RNA. At this point, HIV will integrate its own genome within the host genome (1). The HIV genome contains 9 genes that are specific to its function and survival within the host. These genes code for reverse transcriptase, proteases, and an integrase. Apart from its genome, HIV also replicates at an extremely staggering speed. On HIV molecule can produce billions of copies within a single day (1). Genome Evolution The combination of HIV's extremely fast replication time, high mutation rate, selective pressures from the immune system and reverse transcriptase properties make HIV a well-evolved virus with a very high genetic variability. Interestingly, due to HIV's high genetic variation, a single virus molecule can produce many generations of viruses, each a variant of the parent molecule. The rapid evolution leads to the inability of targeting a specific facet of the virus to cure an infected individual (4). While HIV does have a high mutation, there are certain sequences within the virus that are well conserved between variants and serotypes. Conserved structures include the polyadenylation site (5') and a stem-loop that contains the first protease splice site, which makes the virus active. These structures are also well-conserved between the Simian Immunodeficiency virus (SIV) and HIV. Generally, when certain facets of an organism are well-conserved, it means that they are beneficial to the organisms evolution and survival (3). Due to the relation between SIV and HIV, HIV is believed to have evolved from SIV at an unknown time period. The earliest case of HIV is 1959 (Congo), and the arliest case within the United States is believed to be in 1966 (male presented symptoms, no definitive diagnosis). Many subtypes of HIV and SIV share a common phylogenetic ancestor, as seen in the picture to the right. All subtypes of both SIV and HIV definitively evolved from a common ancestor, more than likely SIV developed first then HIV as humans began to evolve. Time points for these evolutions, however, are unknown. FIV, feline immunodeficiency virus, is similar to HIV and SIV in certain conserved structures, but evolved divergently from SIV and HIV (3). References 1.HIV: The Ultimate Evolver. Understanding Evolution 2. HIV. Wikipedia 3. ''Comparison of SIV and HIV-1 genomic RNA structures reveals impact of sequence evolution on conserved and non-conserved structural motifs. ''PMID: 23593004 4. ''Within-host and between-host evolutionary rates across the HIV-1 genome. ''Retrovirology